upwelling and downwelling fluxes

[jianjun shi]

Dear Rttov:

I am Jun. This task is about how to use RTTOV to calculate infrared upwelling and downwelling radiance fluxes.
I have developed a forward model based on the Eddington second approximation to calculate the top radiance of a dust layer. Therefore, I need the boundary conditions for irradiance of this layer. I would like to know if RTTOV can calculate this values or if there is an approximate method to obtain it. I have searched the literature but haven’t found relevant methods. Additionally, I’m wondering if it’s a reasonable approximation to set the zenith angle as 1/1.66 (infrared diffusivity factor) to obtain irradiance.
Any suggestions and responses are greatly appreciated.

[jianjun shi]

Should I calculate radiance at different angles for the same profile and manually integrate?

[James Hocking]

Hi Jun,

RTTOV is primarily intended to simulated top of atmosphere satellite-seen radiances. It can only compute in-atmosphere upwelling and downwelling radiances for clear sky cases (i.e. excluding aerosols, hydrometeors, etc), and it does not compute irradiances/fluxes at all. Therefore I’m not sure that it can provide you with the boundary conditions you require.

I don’t have experience of using radiance models to approximate fluxes, but I would imagine the best approach is to run simulations over a range of angles and to integrate the results as you suggest.

Best wishes,
James

[Author]

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